(a) Field of the Invention
The present invention relates to a light emitting diode (LED) light emitting device and a method of driving the same. More particularly, the present invention relates to an LED light emitting device that have a DC/DC converter and a constant current source and that include a plurality of LED channels in which a plurality of LEDS are connected in series and a method of driving the same.
(b) Description of the Related Art
A light emitting device can be used for displaying an image, or can be used as a light source of a display device such as a liquid crystal display (LCD). Particularly, a light emitting device that is formed with a plurality of LEDS is widely used as a back light of an LCD. An LED light emitting device includes a plurality of LED channels in which a plurality of LED elements are arranged in series and a DC/DC converter that supplies an output voltage to each of the plurality of LED channels. An output voltage is supplied to one ends of each of the plurality of LED channels, and a constant current source that controls a current flowing to each of the plurality of LED channels is connected to the other end thereof. The constant current source includes a sync current source and controls a current flowing to each of the LED channels using an operating amplifier to be constant.
FIG. 1 is a diagram illustrating an LED light emitting device and illustrates a method of controlling a current flowing to an LED channel using an operating amplifier.
Referring to FIG. 1, the magnitude of a channel current ILED flowing to an LED channel 10 is uniformly controlled by a sync current source 20. Specifically, the sync current source 20 includes an operating amplifier AMP and synchronizes a predetermined channel current ILED according to the output of the operating amplifier AMP. The operating amplifier AMP receives a reference voltage VREF according to a reference resistor Rref and a reference current Iref in a non-inversion terminal (+) and receives a feedback voltage Vfb according to a channel current ILED flowing through a switch M and a detection resistor Rs in an inversion terminal (−). The sync current source 20 controls the channel current ILED so that the reference voltage VREF may be identical to the feedback voltage Vfb. Therefore, the channel current ILED is proportional to the reference current Iref as represented by Equation 1.ILED=(Rref/Rs)*Iref  (Equation 1)
Therefore, the LED channel current ILED can be set to flow in a desired magnitude using the reference current Iref. However, a predetermined offset voltage exists between a non-inversion input terminal (+) and an inversion input terminal (−) of an actual operating amplifier AMP. Further, an error occurs in the magnitude of an actual reference current Iref, a reference resistor Rref, and a detection resistor Rs. Thereby, an error occurs in an LED channel current ILED that is set to a desired magnitude. Further, when a plurality of LED channels are included, errors of an offset voltage, a reference current Iref, a reference resistor Rref, and a detection resistor Rs of each LED channel are different. Therefore, there is a problem that an LED channel current ILED flowing to each LED channel is not same. In order to solve the problem, the detection resistor Rs is formed with a plurality of resistors and is trimmed so that a preset channel current ILED flows at each LED channel. However, in such a method, upon actually trimming, when a channel current of the magnitude different from that of the preset channel current ILED flows, an error occurs between channel currents ILED flowing to each LED channel. Further, there is a method of canceling an offset voltage of the operating amplifier. However, in this method, because an error still exists in the reference current Iref, the reference resistor Rref, and the detection resistor Rs, there is a limitation in uniformly sustaining an LED channel current ILED flowing to each LED channel.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.